Calculating percentage increase is an important skill for geographers to have. When geographers collect data over a period of time, the results may increase. Calculating a percentage increase allows a geographer to see how much their data has changed. For example, it may be useful to find out how much the width of a river channel increases as you travel downstream.
For example: the number of robins in a woodland area are counted over two different months. In December 15 robins were counted. In January 23 robins were counted. What is the percentage increase of robins in the woodland?
Calculating percentage decrease is also a useful skill to have. For example it may be useful to find out how much the load particle size decreases in a river as you travel downstream.
For example: the number of robins in woodland in February and March are counted. In February 22 robins were counted. In March 12 robins were counted. What is the percentage decrease of robins in the woodland?
Percentiles and quartiles are both ways of dividing data into smaller parts. Whereas quartiles divide a set of data into 4 equal parts, percentiles divide the set of data into 100 equal parts.
Percentiles are commonly used to plot the growth of babies. For example, a midwife weighs baby Anna and she is in the 90th percentile. This means that if there were 100 babies (of the same age), 90% of them would weigh the same, or less than baby Anna and 10% would weigh more.